Power control for wireless LAN stations

ABSTRACT

Techniques and apparatus for controlling the transmit power of an uplink (UL) signal from a user terminal in a wireless communications system in an effort to achieve some target characteristic, such as a target carrier-to-interference (C/I) ratio, at an access point (AP) are provided. In this manner, such a user terminal may help avoid or compensate for imbalances in received radio frequency (RF) power between UL signals received from multiple user terminals by the AP. For example, the transmit power at each user terminal may be controlled in an effort to achieve a target post-processing C/I ratio of 28 dB per spatial stream in an effort to reduce large power imbalances and optimize throughput per user terminal. The user terminal and the AP may compose part of a multiple-input multiple-output (MIMO) communication system utilizing spatial-division multiple access (SDMA) techniques.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation application of U.S. patentapplication Ser. No. 12/352,733, filed on Jan. 13, 2009, titled “Powercontrol for wireless LAN stations”, which claims benefit of U.S. PatentProvisional Application No. 61/090,365, filed on Aug. 20, 2008, titled“Power control for SDMA stations” the entireties of which areincorporated herein by reference.

FIELD

Certain embodiments of the present disclosure generally relate towireless communication using multi-antenna transmission for spatialdivision multiple access (SDMA) in a multiple-input multiple-output(MIMO) communication system and, more specifically, to controlling thepower of uplink (UL) signals from multiple SDMA stations in such asystem.

BACKGROUND

In order to address the issue of increasing bandwidth requirementsdemanded for wireless communication systems, different schemes are beingdeveloped to allow multiple user terminals to communicate with a singlebase station by sharing the same channel (same time and frequencyresources) while achieving high data throughputs. Spatial DivisionMultiple Access (SDMA) represents one such approach that has recentlyemerged as a popular technique for the next generation communicationsystems. SDMA techniques may be adopted in several emerging wirelesscommunications standards such as IEEE 802.11 (IEEE is the acronym forthe Institute of Electrical and Electronic Engineers, 3 Park Avenue,17th floor, New York, N.Y.) and Long Term Evolution (LTE).

In SDMA systems, a base station may transmit or receive differentsignals to or from a plurality of mobile user terminals at the same timeand using the same frequency. In order to achieve reliable datacommunication, user terminals may need to be located in sufficientlydifferent directions. Independent signals may be simultaneouslytransmitted from each of multiple space-separated antennas at the basestation. Consequently, the combined transmissions may be directional,i.e., the signal that is dedicated for each user terminal may berelatively strong in the direction of that particular user terminal andsufficiently weak in directions of other user terminals. Similarly, thebase station may simultaneously receive on the same frequency thecombined signals from multiple user terminals through each of multipleantennas separated in space, and the combined received signals from themultiple antennas may be split into independent signals transmitted fromeach user terminal by applying the appropriate signal processingtechnique.

A multiple-input multiple-output (MIMO) wireless system employs a number(N_(T)) of transmit antennas and a number (N_(R)) of receive antennasfor data transmission. A MIMO channel formed by the N_(T) transmit andN_(R) receive antennas may be decomposed into N_(S) spatial channels,where, for all practical purposes, N_(S)≦min{N_(T),N_(R)}. The N_(S)spatial channels may be used to transmit N_(S) independent data streamsto achieve greater overall throughput.

In a multiple-access MIMO system based on SDMA, an access point cancommunicate with one or more user terminals at any given moment. If theaccess point communicates with a single user terminal, then the N_(T)transmit antennas are associated with one transmitting entity (eitherthe access point or the user terminal), and the N_(R) receive antennasare associated with one receiving entity (either the user terminal orthe access point). The access point can also communicate with multipleuser terminals simultaneously via SDMA. For SDMA, the access pointutilizes multiple antennas for data transmission and reception, and eachof the user terminals typically utilizes less than the number of accesspoint antennas for data transmission and reception. When SDMA istransmitted from an access point, N_(S)≦min{N_(T), sum(N_(R))}, wheresum(N_(R)) represents the summation of all user terminal receiveantennas. When SDMA is transmitted to an access point,N_(S)≦min{sum(N_(T)), N_(R)}, where sum(N_(T)) represents the summationof all user terminal transmit antennas.

Orthogonal Frequency Division Multiple Access (OFDMA) is anothertechnique for allowing multiple user terminals to communicate with asingle base station. In an OFDMA-based system, multiple user terminalsmay communicate on different OFDM subcarriers (i.e., differentfrequencies) to a base station.

SUMMARY

Certain embodiments of the present disclosure provide a method for powercontrol of an uplink (UL) signal in a wireless local area network(WLAN). The method generally includes adjusting the power of the ULsignal to meet an access point (AP) target carrier-to-interference (C/I)ratio and transmitting the power-adjusted UL signal.

Certain embodiments of the present disclosure provide a computer-programproduct for power control of a UL signal in a WLAN. The computer-programproduct typically includes a computer-readable medium havinginstructions stored thereon, the instructions being executable by one ormore processors. The instructions generally include instructions foradjusting the power of the UL signal to meet an AP target C/I ratio andinstructions for transmitting the power-adjusted UL signal.

Certain embodiments of the present disclosure provide an apparatus forpower control of a UL signal in a WLAN. The apparatus generally includesmeans for adjusting the power of the UL signal to meet an AP target C/Iratio and means for transmitting the power-adjusted UL signal.

Certain embodiments of the present disclosure provide a mobile devicecapable of power control of a UL signal in a WLAN. The mobile devicegenerally includes logic for adjusting the power of the UL signal tomeet an AP target C/I ratio and a transmitter configured to transmit thepower-adjusted UL signal.

Certain embodiments of the present disclosure provide a method forclosed loop power control of a UL signal in a WLAN. The method generallyincludes receiving a value indicative of the power of the UL signal,determining adjustment information based on at least the received powervalue and a target C/I ratio, and transmitting the adjustmentinformation.

Certain embodiments of the present disclosure provide a computer-programproduct for closed loop power control of a UL signal in a WLAN. Thecomputer-program product typically includes a computer-readable mediumhaving instructions stored thereon, the instructions being executable byone or more processors. The instructions generally include instructionsfor receiving a value indicative of the power of the UL signal,instructions for determining adjustment information based on at leastthe received power value and a target C/I ratio, and instructions fortransmitting the adjustment information.

Certain embodiments of the present disclosure provide an apparatus forclosed loop power control of a UL signal in a WLAN. The apparatusgenerally includes means for receiving a value indicative of the powerof the UL signal, means for determining adjustment information based onat least the received power value and a target C/I ratio, and means fortransmitting the adjustment information.

Certain embodiments of the present disclosure provide an AP capable ofclosed loop power control of a UL signal in a WLAN. The AP generallyincludes a receiver configured to receive a value indicative of thepower of the UL signal, logic for determining adjustment informationbased on at least the received power value and a target C/I ratio, and atransmitter configured to transmit the adjustment information.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the presentdisclosure can be understood in detail, a more particular description,briefly summarized above, may be had by reference to embodiments, someof which are illustrated in the appended drawings. It is to be noted,however, that the appended drawings illustrate only certain typicalembodiments of this disclosure and are therefore not to be consideredlimiting of its scope, for the description may admit to other equallyeffective embodiments.

FIG. 1 illustrates a spatial division multiple access (SDMA)multiple-input multiple-output (MIMO) wireless system, in accordancewith certain embodiments of the present disclosure.

FIG. 2 illustrates a block diagram of an access point (AP) and two userterminals, in accordance with certain embodiments of the presentdisclosure.

FIG. 3 illustrates various components that may be utilized in a wirelessdevice, in accordance with certain embodiments of the presentdisclosure.

FIG. 4 illustrates performance degradation in an interleaved OFDMAscheme for multiple users, in accordance with certain embodiments of thepresent disclosure.

FIG. 5 illustrates example operations for open loop (and optional closedloop) power control of an uplink (UL) signal from the perspective of auser terminal, in accordance with certain embodiments of the presentdisclosure.

FIG. 5A is a block diagram of means corresponding to the exampleoperations of FIG. 5 for UL signal power control, in accordance withcertain embodiments of the present disclosure.

FIGS. 6A and 6B illustrate transmissions of power control information ofan access station, in accordance with certain embodiments of the presentdisclosure.

FIG. 7 illustrates example operations for closed loop power control of aUL signal from the perspective of an AP, in accordance with certainembodiments of the present disclosure.

FIG. 7A is a block diagram of means corresponding to the exampleoperations of FIG. 7 for controlling the power of a UL signal from theperspective of an AP, in accordance with certain embodiments of thepresent disclosure.

DETAILED DESCRIPTION

Certain embodiments of the present disclosure provide techniques andapparatus for controlling the transmit power of an uplink (UL) signalfrom a user terminal in a wireless communications system in an effort toachieve some target characteristic, such as a targetcarrier-to-interference (C/I) ratio, at an access point (AP). In thismanner, such a user terminal may help avoid or compensate for imbalancesin received radio frequency (RF) power between UL signals received frommultiple user terminals by the AP. For example, the transmit power ateach user terminal may be controlled in an effort to achieve a targetpost-processing C/I ratio of 28 dB per spatial stream in an effort toreduce large power imbalances and optimize throughput per user terminal.The user terminal and the AP may compose part of a multiple-inputmultiple-output (MIMO) communication system utilizing spatial-divisionmultiple access (SDMA) techniques.

The word “exemplary” is used herein to mean “serving as an example,instance, or illustration.” Any embodiment described herein as“exemplary” is not necessarily to be construed as preferred oradvantageous over other embodiments. Also as used herein, the term“legacy stations” generally refers to wireless network nodes thatsupport 802.11n or earlier versions of the IEEE 802.11 standard.

The multi-antenna transmission techniques described herein may be usedin combination with various wireless technologies such as Code DivisionMultiple Access (CDMA), Orthogonal Frequency Division Multiplexing(OFDM), Time Division Multiple Access (TDMA), and so on. Multiple userterminals can concurrently transmit/receive data via different (1)orthogonal code channels for CDMA, (2) time slots for TDMA, or (3)sub-bands for OFDM. A CDMA system may implement IS-2000, IS-95, IS-856,Wideband-CDMA (W-CDMA), or some other standards. An OFDM system mayimplement IEEE 802.11 or some other standards. A TDMA system mayimplement GSM or some other standards. These various standards are knownin the art.

An Example MIMO System

FIG. 1 shows a multiple-access MIMO system 100 with access points anduser terminals. For simplicity, only one access point 110 is shown inFIG. 1. An access point (AP) is generally a fixed station thatcommunicates with the user terminals and may also be referred to as abase station or some other terminology. A user terminal (UT) may befixed or mobile and may also be referred to as a mobile station (MS), astation (STA), or some other terminology. A user terminal may be awireless device, such as a cellular phone, a personal digital assistant(PDA), a handheld device, a wireless modem, a laptop computer, apersonal computer, etc.

Access point 110 may communicate with one or more user terminals 120 atany given moment on the downlink and uplink. The downlink (i.e., forwardlink) is the communication link from the access point to the userterminals, and the uplink (i.e., reverse link) is the communication linkfrom the user terminals to the access point. A user terminal may alsocommunicate peer-to-peer with another user terminal. A system controller130 couples to and provides coordination and control for the accesspoints.

While portions of the following disclosure will describe user terminals120 capable of communicating via spatial division multiple access(SDMA), for certain embodiments, the user terminals 120 may also includesome user terminals that do not support SDMA. Thus, for suchembodiments, an AP 110 may be configured to communicate with both SDMAand non-SDMA user terminals. This approach may conveniently allow olderversions of user terminals (“legacy” stations) to remain deployed in anenterprise, extending their useful lifetime, while allowing newer SDMAuser terminals to be introduced as deemed appropriate.

System 100 employs multiple transmit and multiple receive antennas fordata transmission on the downlink and uplink. Access point 110 isequipped with a number N_(ap) of antennas and represents themultiple-input (MI) for downlink transmissions and the multiple-output(MO) for uplink transmissions. A set N_(u) of selected user terminals120 collectively represents the multiple-output for downlinktransmissions and the multiple-input for uplink transmissions. For pureSDMA, it is desired to have N_(ap)≧N_(u)≧1 if the data symbol streamsfor the N_(u) user terminals are not multiplexed in code, frequency, ortime by some means. N_(u) may be greater than N_(ap) if the data symbolstreams can be multiplexed using different code channels with CDMA,disjoint sets of sub-bands with OFDM, and so on. Each selected userterminal transmits user-specific data to and/or receives user-specificdata from the access point. In general, each selected user terminal maybe equipped with one or multiple antennas (i.e., N_(ut)≧1). The N_(u)selected user terminals can have the same or different number ofantennas.

MIMO system 100 may be a time division duplex (TDD) system or afrequency division duplex (FDD) system. For a TDD system, the downlinkand uplink share the same frequency band. For an FDD system, thedownlink and uplink use different frequency bands. MIMO system 100 mayalso utilize a single carrier or multiple carriers for transmission.Each user terminal may be equipped with a single antenna (e.g., in orderto keep costs down) or multiple antennas (e.g., where the additionalcost can be supported).

FIG. 2 shows a block diagram of access point 110 and two user terminals120 m and 120 x in MIMO system 100. Access point 110 is equipped withN_(ap) antennas 224 a through 224 ap. User terminal 120 m is equippedwith N_(ut,m) antennas 252 ma through 252 mu, and user terminal 120 x isequipped with N_(ut,x) antennas 252 xa through 252 xu. Access point 110is a transmitting entity for the downlink and a receiving entity for theuplink. Each user terminal 120 is a transmitting entity for the uplinkand a receiving entity for the downlink. As used herein, a “transmittingentity” is an independently operated apparatus or device capable oftransmitting data via a wireless channel, and a “receiving entity” is anindependently operated apparatus or device capable of receiving data viaa wireless channel. In the following description, the subscript “dn”denotes the downlink, the subscript “up” denotes the uplink, N_(up) userterminals are selected for simultaneous transmission on the uplink,N_(dn) user terminals are selected for simultaneous transmission on thedownlink, N_(up) may or may not be equal to N_(dn), and N_(up) andN_(dn) may be static values or can change for each scheduling interval.The beam-steering or some other spatial processing technique may be usedat the access point and user terminal.

On the uplink, at each user terminal 120 selected for uplinktransmission, a TX data processor 288 receives traffic data from a datasource 286 and control data from a controller 280. TX data processor 288processes (e.g., encodes, interleaves, and modulates) the traffic data{d_(up,m)} for the user terminal based on the coding and modulationschemes associated with the rate selected for the user terminal andprovides a data symbol stream {s_(up,m)}. A TX spatial processor 290performs spatial processing on the data symbol stream {s_(up,m)} andprovides N_(ut,m) transmit symbol streams for the N_(ut,m) antennas.Each transmitter unit (TMTR) 254 receives and processes (e.g., convertsto analog, amplifies, filters, and frequency upconverts) a respectivetransmit symbol stream to generate an uplink signal. N_(ut,m)transmitter units 254 provide N_(ut,m) uplink signals for transmissionfrom N_(ut,m) antennas 252 to the access point 110.

A number N_(up) of user terminals may be scheduled for simultaneoustransmission on the uplink. Each of these user terminals performsspatial processing on its data symbol stream and transmits its set oftransmit symbol streams on the uplink to the access point.

At access point 110, N_(ap) antennas 224 a through 224 ap receive theuplink signals from all N_(up) user terminals transmitting on theuplink. Each antenna 224 provides a received signal to a respectivereceiver unit (RCVR) 222. Each receiver unit 222 performs processingcomplementary to that performed by transmitter unit 254 and provides areceived symbol stream. An RX spatial processor 240 performs receiverspatial processing on the N_(ap) received symbol streams from N_(ap)receiver units 222 and provides N_(up) recovered uplink data symbolstreams. The receiver spatial processing is performed in accordance withthe channel correlation matrix inversion (CCMI), minimum mean squareerror (MMSE), successive interference cancellation (SIC), or some othertechnique. Each recovered uplink data symbol stream {s_(up,m)} is anestimate of a data symbol stream {s_(up,m)} transmitted by a respectiveuser terminal. An RX data processor 242 processes (e.g., demodulates,deinterleaves, and decodes) each recovered uplink data symbol stream{s_(up,m)} in accordance with the rate used for that stream to obtaindecoded data. The decoded data for each user terminal may be provided toa data sink 244 for storage and/or a controller 230 for furtherprocessing.

On the downlink, at access point 110, a TX data processor 210 receivestraffic data from a data source 208 for N_(dn) user terminals scheduledfor downlink transmission, control data from a controller 230, andpossibly other data from a scheduler 234. The various types of data maybe sent on different transport channels. TX data processor 210 processes(e.g., encodes, interleaves, and modulates) the traffic data for eachuser terminal based on the rate selected for that user terminal. TX dataprocessor 210 provides N_(dn) downlink data symbol streams for theN_(dn) user terminals. A TX spatial processor 220 performs spatialprocessing on the N_(dn) downlink data symbol streams, and providesN_(ap) transmit symbol streams for the N_(ap) antennas. Each transmitterunit (TMTR) 222 receives and processes a respective transmit symbolstream to generate a downlink signal. N_(ap) transmitter units 222provide N_(ap) downlink signals for transmission from N_(ap) antennas224 to the user terminals.

At each user terminal 120, N_(ut,m) antennas 252 receive the N_(ap)downlink signals from access point 110. Each receiver unit (RCVR) 254processes a received signal from an associated antenna 252 and providesa received symbol stream. An RX spatial processor 260 performs receiverspatial processing on N_(ut,m) received symbol streams from N_(ut,m)receiver units 254 and provides a recovered downlink data symbol stream{s_(dn,m)} for the user terminal. The receiver spatial processing isperformed in accordance with the CCMI, MMSE, or some other technique. AnRX data processor 270 processes (e.g., demodulates, deinterleaves, anddecodes) the recovered downlink data symbol stream to obtain decodeddata for the user terminal.

At each user terminal 120, N_(ut,m) antennas 252 receive the N_(ap)downlink signals from access point 110. Each receiver unit (RCVR) 254processes a received signal from an associated antenna 252 and providesa received symbol stream. An RX spatial processor 260 performs receiverspatial processing on N_(ut,m) received symbol streams from N_(ut,m)receiver units 254 and provides a recovered downlink data symbol stream{s_(dn,m)} for the user terminal. The receiver spatial processing isperformed in accordance with the CCMI, MMSE, or some other technique. AnRX data processor 270 processes (e.g., demodulates, deinterleaves, anddecodes) the recovered downlink data symbol stream to obtain decodeddata for the user terminal.

FIG. 3 illustrates various components that may be utilized in a wirelessdevice 302 that may be employed within the system 100. The wirelessdevice 302 is an example of a device that may be configured to implementthe various methods described herein. The wireless device 302 may be anaccess point 110 or a user terminal 120.

The wireless device 302 may include a processor 304 which controlsoperation of the wireless device 302. The processor 304 may also bereferred to as a central processing unit (CPU). Memory 206A, which mayinclude both read-only memory (ROM) and random access memory (RAM),provides instructions and data to the processor 304. A portion of thememory 206A may also include non-volatile random access memory (NVRAM).The processor 304 typically performs logical and arithmetic operationsbased on program instructions stored within the memory 206A. Theinstructions in the memory 206A may be executable to implement themethods described herein.

The wireless device 302 may also include a housing 308 that may includea transmitter 310 and a receiver 312 to allow transmission and receptionof data between the wireless device 302 and a remote location. Thetransmitter 310 and receiver 312 may be combined into a transceiver 314.A plurality of transmit antennas 316 may be attached to the housing 308and electrically coupled to the transceiver 314. The wireless device 302may also include (not shown) multiple transmitters, multiple receivers,and multiple transceivers.

The wireless device 302 may also include a signal detector 318 that maybe used in an effort to detect and quantify the level of signalsreceived by the transceiver 314. The signal detector 318 may detect suchsignals as total energy, energy per subcarrier per symbol, powerspectral density and other signals. The wireless device 302 may alsoinclude a digital signal processor (DSP) 320 for use in processingsignals.

The various components of the wireless device 302 may be coupledtogether by a bus system 322, which may include a power bus, a controlsignal bus, and a status signal bus in addition to a data bus.

Power Control for 802.11 Stations for Multiple Access

The next generation of the IEEE 802.11 standard is moving towards SDMAand Orthogonal Frequency-Division Multiple Access (OFDMA). Thesetechnologies include provisions for multiple stations (STAs) to besimultaneously transmitting to an access point (AP). However, largepower imbalances in the received power from multiple stations may resultin performance degradation due to signal-dependent RF noise floors andfrequency offset. For example, each AP-STA link may have differentfrequency offsets, which may lead to inter-channel interference (ICI)distortion. The signal-dependent RF noise floors may arise from I-Qimbalance and RF nonlinearities in each STA.

For example, FIG. 4 illustrates performance degradation in aninterleaved OFDMA scheme with uplink (UL) signals from four users. InFIG. 4, three of the four user UL signal tones are power-boosted OFDMAUL signal tones 401, 402, 403, while the desired user UL signal 404 isnot power-boosted in the same manner and, thus, has a lower power level.Such large uplink power differences across user terminals may lead toincreased performance degradation for user terminals with lower receivedOFDMA signal power at the AP. To the first order, even largerperformance degradation may be expected from SDMA power imbalances.

As shown, tones adjacent to power-boosted OFDMA (or SDMA) tones 401,402, 403 may suffer from ICI distortion 406 (due to frequency offseterror) and from phase noise distortion 408. Furthermore, tones 412 thatare mirrors of OFDMA (or SDMA) power-boosted users may suffer from I-Qimbalance distortion 410 above the thermal noise floor 414.

Accordingly, what is needed are techniques and apparatus for controllingthe power of uplink signals from multiple user terminals in an effort toreduce power degradation at an access point, especially for userterminals with lower received signal power at the AP.

Example Open Loop Power Control

FIG. 5 illustrates example operations 500 for power control of a ULsignal from the perspective of a user terminal, according to certainembodiments of the present disclosure. The operations 500 may begin, at510, by adjusting the power of a UL signal to meet a targetcarrier-to-interference (C/I) ratio of an access point (AP). Thisadjustment at 510 may be performed by the user terminal upon receptionof DL packets and prior to UL multiple access transmission. The AP'starget C/I ratio may be a post-processing target such that the targetC/I ratio reflects a desired C/I ratio of a UL signal received from anycapable user terminal after reception and signal processing by the AP.For some embodiments, the transmit power of a UL signal may be adjustedto meet the AP target C/I ratio and a client peak power constraint

For some embodiments, the target C/I ratio may be 28 dB per spatialstream in an effort to maximize throughput per user terminal. Although atarget C/I ratio of 28 dB may yield a heightened spectral efficiency,the target C/I ratio may change depending on the code-rate used.Furthermore, for link-budget limited user terminals, a C/I ratio of 28dB may not be achievable due to power amplifier (PA) limitations in thetransmitter.

To meet the target C/I ratio at the AP, the user terminal's transmitpower (P_(client)) for the UL signal may be calculated at 510 accordingto the following formula:P _(client)=SNR_(Target) −G _(OFDMA) −G _(SDMA) −G _(CDMA) +N _(TH) +C+P_(AP)−RSSI_(client)where SNR_(Target) is the target C/I ratio at the AP, G_(OFDMA) is anoptional orthogonal frequency-division multiple access (OFDMA)processing gain, G_(SDMA) is an optional spatial-division multipleaccess (SDMA) processing gain at the AP, G_(CDMA) is an optionalcode-division multiple access (CDMA) processing gain, N_(TH) is athermal noise floor, C represents parameters calibrated duringassociation or other representative packet exchange protocols, P_(AP) isan AP transmit power (e.g., advertised by the AP), and RSSI_(client) isa received signal strength indication (RSSI) of a received downlink (DL)signal measured at the user terminal. Some of these parameters may becalibrated out, and other parameters may be provided by the AP, forexample.

The calculation for P_(client) may most likely include at least one ofG_(OFDMA), G_(SDMA), and G_(CDMA). G_(OFDMA) may be equal to 10log₁₀(64/N_(tones)) where N_(tones) is the number of frequencies usedfor transmission, and G_(SDMA) may be equal to 10 log₁₀(M_(T)/N_(S))where M_(T) is the number of transmit antennas and N_(S) is the numberof SDMA spatial streams. The parameters calibrated during association orother representative packet exchange protocols may include, for example,a noise figure at the AP (NF_(AP)) and a radio frequency (RF)/antennagain at the AP (G_(AP,RF)). Such parameters may be advertised by the AP.

At 520, the user terminal may transmit the power-adjusted UL signal. Thetransmitted signal may meet the calculated transmit power P_(client),for example, unless the desired power exceeds the capabilities of thetransmitter circuit components, such as the power amplifier. In thismanner, the UL signal may be received by an AP and, afterpost-processing, may achieve the desired target C/I ratio. If multipleuser terminals implement the operations at 510 and 520 described abovein an effort to transmit multiple UL signals attempting to meet thedesired AP target C/I ratio, there need not be large power differencesbetween the UL signals received by the AP, and the performancedegradation to UL signals with lower received signal power may mostlikely be reduced. In other words, according to certain embodiments ofthe present disclosure, by having the transmit power of UL signals fromdifferent user terminals adjusted to meet a target C/I ratio at the AP,significant differences in received UL signal power may be eliminated,and the effects of ICI distortion, phase distortion, and I-Q imbalance,for example, may be mitigated.

Example Closed Loop Power Control

The operations at 510 and 520 may be considered as open loop powercontrol operations because these operations adjust the transmit power ofUL signals without feedback from the AP. However, as illustrated byoptional operations at 530 to 550, closed loop operations (based on APfeedback) may also be performed. Closed loop power control may beemployed in an effort to provide better power control and account forany imperfections in open loop power control due to, for example, animperfect or outdated RSSI measurement and any changes to AP RF andprocessing gains. Further, closed loop power control may allow the AP tomanage client transmit powers for optimum UL SDMA/OFDMA performance,police rogue clients (i.e., clients that are transmitting with excessivepower, perhaps due to incorrect RSSI measurements or estimates), andlimit interference generated to neighbor base station subsystems (BSSs),for example, in enterprise applications.

Therefore, for closed loop power control operations as illustrated inFIG. 6A, the user terminal 120 may transmit a value 600 (e.g.,P_(client)) indicative of the power of the power-adjusted UL signal at530. At 540, the user terminal 120 may receive adjustment information650 (represented as ΔP) from the AP 110 as shown in FIG. 6B. For someembodiments, the adjustment information 650 may be based on the powervalue 600 and the target C/I ratio of the AP 110. For example, theadjustment information 650 may be a new, adjusted target C/I ratio(e.g., SNR_(Target)′) or an adjustment to the target C/I ratio (e.g.,ΔSNR_(Target)) based on the difference between the target C/I ratio andthe actual received C/I after post-processing. At 550, the user terminal120 may adjust the transmit power of the UL signal based on theadjustment information 650 received from the AP 110.

For certain embodiments, the user terminal 120 may communicate thecurrently used transmit power value 600, such as P_(client), in units ofdBm, for example, to the AP 110 using an N-bit field in a Media AccessControl (MAC) header of a UL packet such that bit values ranging from 0to 2^(N)−1 indicate representative values. In such a scenario with N=6as an example, the bit-representation may cover a range of [0:1:63]corresponding to a power value 600 ranging from [−8.5:0.5:23.0] dBm, forexample, with a resolution of 0.5 dBm, for some embodiments.

For other embodiments, the power value 600 communicated by the userterminal 120 may represent a back-off value from a peak transmit power.This feedback may allow the AP 110 to determine the amount of PAheadroom available to the user terminal 120. Such information may beneeded for DL closed-loop power control signaling for multiple stations.Hence, a range of [0:1:63] with N=6, for example, may correspond to apeak transmit power that is [0.0:0.5:31.5] dB below the peak transmitpower with a resolution of 0.5 dB. The user terminal 120 may communicatethe peak transmit power to the AP 110 during association, the initialhandshake when the user terminal 120 first enters the network.

FIG. 7 illustrates example operations 700 for closed loop power controlof a UL signal from the perspective of an AP 110. The operations 700 maybegin, at 710, by receiving a value 600 (e.g., P_(client) as shown inFIG. 6A) indicative of the power of a UL signal transmitted by a userterminal 120. The AP 110 may be able to decode the power value in a MACheader of a received UL packet.

At 720, the AP 110 may determine adjustment information 650 based on atleast the received power value 600 and a target C/I ratio. For example,the adjustment information 650 may be a new, adjusted target C/I ratio(e.g., SNR_(Target)′) or an adjustment to the target C/I ratio (e.g.,ΔSNR_(Target)) based on the difference between the target C/I ratio andthe measured C/I of the UL signal after reception at 710 andpost-processing. For some embodiments, the AP target C/I ratio may be 28dB per spatial stream as described above.

At 730, the AP 110 may transmit the adjustment information 650 (e.g., APas shown in FIG. 6B) to the user terminal 120. To communicate theadjustment information 650, the AP 110 may encode the adjustmentinformation 650 in a MAC header of a DL packet. For certain embodiments,the AP 110 may use an M-bit field in the MAC header of the DL packetsuch that bit values ranging from 0 to 2^(M)−1 indicate representativevalues. In such a scenario with M=6 as an example, thereby covering arange of [0:1:63], the bit-representation may correspond to anadjustment range of [46.0:0.5:15.5] dBm for some embodiments.

For other embodiments, the adjustment information 650 communicated tothe user terminal 120 may represent a back-off value from a peaktransmit power. As noted above, the adjustment information 650 may takeinto account the PA headroom available to the user terminal 120. Hence,a range of [0:1:63] with M=6, for example, may correspond to a transmitpower that is [0.0:0.5:31.5] dB below the peak transmit power with aresolution of 0.5 dB.

The operations 700 may be performed for multiple user terminals, each ofwhich may provide a value indicative of transmit power used for ULtransmissions. Thus, the AP may send different power adjustmentinformation to different user terminals.

The various operations of methods described above may be performed byvarious hardware and/or software component(s) and/or module(s)corresponding to means-plus-function blocks illustrated in the figures.Generally, where there are methods illustrated in figures havingcorresponding counterpart means-plus-function figures, the operationblocks correspond to means-plus-function blocks with similar numbering.For example, blocks 510-550 illustrated in FIG. 5 correspond tomeans-plus-function blocks 510A-550A illustrated in FIG. 5A. Similarly,blocks 710-730 of FIG. 7 correspond to means-plus-function blocks710A-730A illustrated in FIG. 7A.

As used herein, the term “determining” encompasses a wide variety ofactions. For example, “determining” may include calculating, computing,processing, deriving, investigating, looking up (e.g., looking up in atable, a database or another data structure), ascertaining, and thelike. Also, “determining” may include receiving (e.g., receivinginformation), accessing (e.g., accessing data in a memory), and thelike. Also, “determining” may include resolving, selecting, choosing,establishing, and the like.

Information and signals may be represented using any of a variety ofdifferent technologies and techniques. For example, data, instructions,commands, information, signals, and the like that may be referencedthroughout the above description may be represented by voltages,currents, electromagnetic waves, magnetic fields or particles, opticalfields or particles, or any combination thereof.

The various illustrative logical blocks, modules, and circuits describedin connection with the present disclosure may be implemented orperformed with a general purpose processor, a digital signal processor(DSP), an application specific integrated circuit (ASIC), a fieldprogrammable gate array signal (FPGA) or other programmable logic device(PLD), discrete gate or transistor logic, discrete hardware components,or any combination thereof designed to perform the functions describedherein. A general purpose processor may be a microprocessor, but in thealternative, the processor may be any commercially available processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

The steps of a method or algorithm described in connection with thepresent disclosure may be embodied directly in hardware, in a softwaremodule executed by a processor, or in a combination of the two. Asoftware module may reside in any form of storage medium that is knownin the art. Some examples of storage media that may be used includerandom access memory (RAM), read only memory (ROM), flash memory, EPROMmemory, EEPROM memory, registers, a hard disk, a removable disk, aCD-ROM and so forth. A software module may comprise a singleinstruction, or many instructions, and may be distributed over severaldifferent code segments, among different programs, and across multiplestorage media. A storage medium may be coupled to a processor such thatthe processor can read information from, and write information to, thestorage medium. In the alternative, the storage medium may be integralto the processor.

The methods disclosed herein comprise one or more steps or actions forachieving the described method. The method steps and/or actions may beinterchanged with one another without departing from the scope of theclaims. In other words, unless a specific order of steps or actions isspecified, the order and/or use of specific steps and/or actions may bemodified without departing from the scope of the claims.

The functions described may be implemented in hardware, software,firmware, or any combination thereof. If implemented in software, thefunctions may be stored as one or more instructions on acomputer-readable medium. A storage media may be any available mediathat can be accessed by a computer. By way of example, and notlimitation, such computer-readable media can comprise RAM, ROM, EEPROM,CD-ROM or other optical disk storage, magnetic disk storage or othermagnetic storage devices, or any other medium that can be used to carryor store desired program code in the form of instructions or datastructures and that can be accessed by a computer. Disk and disc, asused herein, include compact disc (CD), laser disc, optical disc,digital versatile disc (DVD), floppy disk, and Blu-ray® disc where disksusually reproduce data magnetically, while discs reproduce dataoptically with lasers.

Software or instructions may also be transmitted over a transmissionmedium. For example, if the software is transmitted from a website,server, or other remote source using a coaxial cable, fiber optic cable,twisted pair, digital subscriber line (DSL), or wireless technologiessuch as infrared, radio, and microwave, then the coaxial cable, fiberoptic cable, twisted pair, DSL, or wireless technologies such asinfrared, radio, and microwave are included in the definition oftransmission medium.

Further, it should be appreciated that modules and/or other appropriatemeans for performing the methods and techniques described herein can bedownloaded and/or otherwise obtained by a user terminal and/or basestation as applicable. For example, such a device can be coupled to aserver to facilitate the transfer of means for performing the methodsdescribed herein. Alternatively, various methods described herein can beprovided via storage means (e.g., RAM, ROM, a physical storage mediumsuch as a compact disc (CD) or floppy disk, etc.), such that a userterminal and/or base station can obtain the various methods uponcoupling or providing the storage means to the device. Moreover, anyother suitable technique for providing the methods and techniquesdescribed herein to a device can be utilized.

It is to be understood that the claims are not limited to the preciseconfiguration and components illustrated above. Various modifications,changes and variations may be made in the arrangement, operation anddetails of the methods and apparatus described above without departingfrom the scope of the claims.

The invention claimed is:
 1. A method for power control of an uplink(UL) signal in a wireless local area network (WLAN), the methodcomprising: receiving, at a user terminal, a downlink (DL) signal froman access point (AP) of the WLAN; measuring, at the user terminal, areceived signal strength of the DL signal; calculating a desiredtransmit power of the user terminal for transmitting the UL signal basedat least on a target signal-to-noise ratio at the AP, a processing gainat the AP, and the received signal strength of the DL signal, whereinthe processing gain at the AP is a function of at least one of: a numberof frequencies used for transmission or a number of spatial streams;adjusting a transmit power of the UL signal to an adjusted transmitpower based on the desired transmit power; encoding an indication of avalue of the adjusted transmit power in a header of an UL packet; andtransmitting the UL signal, at the adjusted transmit power, to the AP,wherein the UL signal includes the UL packet.
 2. The method of claim 1,further comprising: determining whether the desired transmit powerexceeds a capability of one or more transmitter circuit components ofthe user terminal; and if not setting the adjusted transmit power to thedesired transmit power.
 3. The method of claim 1, wherein the processinggain is an orthogonal frequency-division multiple access (OFDMA)processing gain at the AP.
 4. The method of claim 1, wherein theprocessing gain is a spatial-division multiple access (SDMA) processinggain at the AP.
 5. The method of claim 1, wherein the processing gain isa code-division multiple access (CDMA) processing gain at the AP.
 6. Themethod of claim 1, wherein calculating the desired transmit power of theuser terminal for transmitting the UL signal is based at least on thetarget signal-to-noise ratio at the AP, the processing gain at the AP,the received signal strength of the DL signal, and a thermal noise floorparameter.
 7. The method of claim 1, wherein calculating the desiredtransmit power of the user terminal for transmitting the UL signal isbased at least on the target signal-to-noise ratio at the AP, theprocessing gain at the AP, the received signal strength of the DLsignal, and a parameter indicating a transmit power of the AP, whereinthe parameter indicating the transmit power of the AP is advertised bythe AP.
 8. The method of claim 1, wherein calculating the desiredtransmit power of the user terminal for transmitting the UL signal isbased at least on the target signal-to-noise ratio at the AP, theprocessing gain at the AP, the received signal strength of the DLsignal, and one or more additional parameters calibrated during anassociation of the user terminal with the AP.
 9. The method of claim 1,wherein encoding the indication of the value of the adjusted transmitpower comprises encoding the indication of the value in a Media AccessControl (MAC) header of the UL packet.
 10. The method of claim 1,further comprising: communicating a peak transmit power of the userterminal to the AP during an association of the user terminal with theAP, wherein the indication of the value of the adjusted transmit powerrepresents an amount that the adjusted transmit power is below the peaktransmit power of the user terminal.
 11. The method of claim 1, furthercomprising: receiving adjustment information from the AP in response totransmitting the UL signal to the AP; and adjusting the transmit powerof a subsequent UL signal to an updated adjusted transmit power based onthe adjustment information.
 12. The method of claim 11, wherein theadjustment information indicates at least one of a new targetsignal-to-noise ratio at the AP or an adjustment to the targetsignal-to-noise ratio at the AP.
 13. The method of claim 11, furthercomprising: communicating a peak transmit power of the user terminal tothe AP during an association of the user terminal with the AP, whereinthe adjustment information represents back-off value from the peaktransmit power.
 14. A method for power control of an uplink (UL) signalin a wireless local area network (WLAN), the method comprising:transmitting, by an access point (AP), a downlink (DL) signal to a userterminal of the WLAN; receiving, at the AP, the UL signal from the userterminal, wherein the UL signal comprises a UL packet; decoding a headerof the UL packet to retrieve an indication of a value of an adjustedtransmit power of the UL signal, wherein the value of the adjustedtransmit power is based on a target signal-to-noise ratio at the AP, aprocessing gain at the AP, and a received signal strength of the DLsignal measured by the user terminal, wherein the processing gain at theAP is a function of at least one of: a number of frequencies used fortransmission or a number of spatial streams; determining an actualsignal-to-noise ratio of the UL signal received at the AP; comparing theactual signal-to-noise ratio of the UL signal to the targetsignal-to-noise ratio to generate adjustment information for adjustingthe transmit power of subsequent UL signals by the user terminal; andtransmitting the adjustment information to the user terminal.
 15. Themethod of claim 14, wherein the adjustment information indicates atleast one of a new target signal-to-noise ratio at the AP or anadjustment to the target signal-to-noise ratio at the AP.
 16. The methodof claim 14, further comprising: receiving, at the AP, during anassociation of the user terminal with the AP, a value of a peak transmitpower of the user terminal, wherein the adjustment informationrepresents a back-off value from the peak transmit power of the userterminal.
 17. The method of claim 14, further comprising: communicating,by the AP to the user terminal, during an association of the userterminal with the AP, at least one parameter selected from the groupconsisting of: an orthogonal frequency-division multiple access (OFDMA)processing gain at the AP, a spatial-division multiple access (SDMA)processing gain at the AP, a code-division multiple access (CDMA)processing gain at the AP, a thermal noise floor parameter, and a valueof a transmit power of the AP, wherein the value of the adjustedtransmit power is based on the target signal-to-noise ratio at the AP,the received signal strength of the DL signal measured by the userterminal, and the at least one parameter.
 18. A user terminal,comprising: at least one processor; and memory coupled to the at leastone processor, wherein the at least one processor and the memory areconfigured to direct the wireless device to: receive, at the userterminal, a downlink (DL) signal from an access point (AP) of a wirelesslocal area network (WLAN); measure, at the user terminal, a receivedsignal strength of the DL signal; calculate a desired transmit power ofthe user terminal for transmitting the UL signal based at least on atarget signal-to-noise ratio at the AP, a processing gain at the AP, andthe received signal strength of the DL signal, wherein the processinggain at the AP is a function of at least one of: a number of frequenciesused for transmission or a number of spatial streams; adjust a transmitpower of the UL signal to an adjusted transmit power based on thedesired transmit power; encode an indication of a value of the adjustedtransmit power in a header of an UL packet; and transmit the UL signal,at the adjusted transmit power, to the AP, wherein the UL signalincludes the UL packet.
 19. The user terminal of claim 18, wherein theat least one processor and the memory are further configured to directthe wireless device to: receive adjustment information from the AP inresponse to transmitting the UL signal to the AP; and adjust thetransmit power of a subsequent UL signal to an updated adjusted transmitpower based on the adjustment information.
 20. The user terminal ofclaim 19, wherein the adjustment information indicates at least one of anew target signal-to-noise ratio at the AP or an adjustment to thetarget signal-to-noise ratio at the AP.
 21. The user terminal of claim19, wherein the at least one processor and the memory are furtherconfigured to direct the wireless device to: communicate a peak transmitpower of the user terminal to the AP during an association of the userterminal with the AP, wherein the adjustment information representsback-off value from the peak transmit power.
 22. An access point (AP),comprising: at least one processor; and memory coupled to the at leastone processor, wherein the at least one processor and the memory areconfigured to direct the AP to: transmitting, by the AP, a downlink (DL)signal to a user terminal of a wireless local area network (WLAN);receive, at the AP, the UL signal from the user terminal, wherein the ULsignal comprises a UL packet; decode a header of the UL packet toretrieve an indication of a value of an adjusted transmit power of theUL signal, wherein the value of the adjusted transmit power is based ona target signal-to-noise ratio at the AP, a processing gain at the AP,and a received signal strength of the DL signal measured by the userterminal, wherein the processing gain at the AP is a function of atleast one of: a number of frequencies used for transmission or a numberof spatial streams; determine an actual signal-to-noise ratio of the ULsignal received at the AP; compare the actual signal-to-noise ratio ofthe UL signal to the target signal-to-noise ratio to generate adjustmentinformation for adjusting the transmit power of subsequent UL signals bythe user terminal; and transmit the adjustment information to the userterminal.
 23. The access point of claim 22, wherein the adjustmentinformation indicates at least one of a new target signal-to-noise ratioat the AP or an adjustment to the target signal-to-noise ratio at theAP.
 24. The access point of claim 22, wherein the at least one processand the memory are further configured to direct the AP to: receive, atthe AP, during an association of the user terminal with the AP, a valueof a peak transmit power of the user terminal, wherein the adjustmentinformation represents a back-off value from the peak transmit power ofthe user terminal.